Typing: Accept non-standard logger in helpers logging something

[k4nar]

I’m using structlog for logging, and mypy is not happy when I’m passing my logger to one of the logging utils:

 error: Argument 1 to "before_sleep_log" has incompatible type "BoundLogger"; expected "Logger"  [arg-type]

This PR introduces a Protocol to accept anything looking like a logger.

Example:

from tenacity import before_log

import logging
before_log(logging.getLogger(), logging.INFO)


import structlog
before_log(structlog.get_logger(), logging.INFO)


import loguru
before_log(loguru.logger, logging.INFO)

$ uv run --with mypy,structlog,loguru mypy example.py
Success: no issues found in 1 source file